There is known an amplifier of a capacitance feedback type, in which input/output terminals are connected via a capacitor. FIG. 10 of JP-A 2-210859 discloses an amplification circuit in which two capacitors, having substantially the same upper electrodes and lower electrodes, are provided in a feedback path with the upper electrode of one of the capacitors connected to the lower electrode of the other capacitor. With this configuration, it is possible to improve linearity of the output of the amplification circuit.
Assume that the amplification circuit disclosed in JP-A 2-210859 receives signals from an input capacitance. In this case, the gain of the amplification circuit is calculated by a ratio between a capacitance value of the input capacitance and a capacitance value of a feedback capacitance.
The capacitance value of the input capacitance, however, changes according to the magnitude of applied bias (bias dependency of capacitance value). Therefore, the gain of the amplification circuit changes according to the amplitude of signals retained by the input capacitance, thereby decreasing the linearity of the output of the amplification circuit.
The present invention has been made to solve the above problems.